mentioned in the previous section, it seems in practice that different simple programs usually agree quite well in their ability or inability to find short descriptions.

But this seems to be considerably less true when one is dealing with descriptions in which information can be lost. For it is rather common to see cases in which only a few features of a system may be difficult to describe—and depending on whether or not a given program happens to be sensitive to these features it can ascribe either a quite high or a quite low complexity to the system.

Nevertheless, as a practical matter, by far the most common way in which we determine levels of complexity is by using our eyes and our powers of visual perception. So in practice what we most often mean when we say that something seems complex is that the particular processes that are involved in human visual perception have failed to extract a short description.

And indeed I suspect that even below the level of conscious thought our brains already have a rather definite notion of complexity. For when we are presented with a complex image, our eyes tend to dwell on it, presumably in an effort to give our brains a chance to extract a simple description.

If we can find no simple features whatsoever—as in the case of perfect randomness—then we tend to lose interest. But somehow the images that draw us in the most—and typically that we find the most aesthetically pleasing—are those for which some features are simple for us to describe, but others have no short description that can be found by any of our standard processes of visual perception.

Before the discoveries in this book, one might have thought that to create anything with a significant level of apparent complexity would necessarily require a procedure which itself had significant complexity. But what we have discovered in this book is that in fact there are remarkably simple programs that produce behavior of great complexity. And what this means—as the images in this book repeatedly demonstrate—is that in the end it is rather easy to make pictures for which our visual system can find no simple overall description.